Radiant heater

ABSTRACT

A thick film, large area resistance heater including a substrate having an electrically non-conductive surface on which is deposited a film electrical resistor such as a thermally sprayed, photo resist etched foil or sol-gel graphite based material. A combination of an electrically conductive film coated backer board substrate composed of portland cement, sand, cellulose fibers and other selected additives. A mica substrate heater can be cemented to a cement backer board or a vinyl with adhesive backing.

BACKGROUND OF THE INVENTION

This invention relates to heaters and in particular to a method ofheating rooms and spaces through radiant heat from floors, walls andceilings. There are various known systems and methods used for heatingfloors. Some include circulating heated water or air through a pipingsystem installed beneath the surface of the floor (FIG. 1). Othersinclude electrically heated insulated wires that are enmeshed in amaterial placed in between the floor surface and the sub floor, or in aconcrete layer that also serves as the finished floor. In otherinstances a cement board is attached to the sub floor and a finishmaterial such as tile, linoleum or wood are adhered to the cement board.In those systems efficiency is compromised as there is no intimatecontact between the source of heat and the surface to be heated. Thisinvention overcomes these shortcomings of the prior art, and provides animproved system for heating surfaces such as floors and walls.

SUMMARY OF THE INVENTION

This invention meets the need for a more efficient, space saving, costefficient and energy saving method to heat floors, walls, ceilings andsurface areas such as countertops. In one preferred embodiment, aresistive film such is applied directly to a backer board by means ofspraying, painting or silk screening where the tile or outer surfacematerial is to be applied.

The width and thickness of the resistive film is selected to provide thedesired power as expressed in watts per square inch or watts per squarefoot. In embodiments utilizing a resistive material, the materialrequires a firing process for curing. During the curing process it isnecessary to control the process so that the cement backer board is notheated sufficiently to degrade the materials within the backer board. Inone preferred embodiment the resistive film is cured by the use ofinfra-red heat processing equipment.

In another preferred embodiment the resistive film can be patterned ontoan insulative material substrate such as mica, and the mica interposedbetween the subfloor and the finish surface material such as tile orlinoleum. In this embodiment the mica is installed by the use of anadhesive applied to the backer board and to the finish surface material.The mica can be in the form of pre-cut tiles with the resistive materialpatterned onto each tile.

After the resistive material is applied and cured, spaced apartelectrodes or bus-bars are applied to apply a voltage across thepatterned resistive material. A protective coating such as Teflon® orsilicon is then applied over the resistive material to protect it frommoisture and to provide an electrically insulative layer.

In another aspect of the invention, overheating can be prevented by theuse of a temperature sensor embedded in or placed atop the floorassembly. The sensor sends a signal to a controller that reduces or cutspower if a maximum temperature is reached or exceeded. These and otherfeatures of the invention will be described below and in reference tothe drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a prior art radiant heatingassembly.

FIG. 2 is a top plan view of a preferred embodiment of the invention.

FIG. 3 is a cross-sectional view of the embodiment shown in FIG. 1 shownas part of a floor assembly.

FIG. 4 is a cross-sectional view of the embodiment shown in FIG. 4 andwhich also includes a decorative top layer over the heating unit.

FIG. 5 is a top plan view of a second embodiment of the invention whichuses a different interconnect.

FIG. 6 is a top plan view of the embodiment of the invention shown inFIG. 2 in which multiple individual units are shown interconnected.

DETAILED DESCRIPTION

Referring now to FIGS. 2-4, a preferred embodiment of the invention isshown generally at 10, and includes a backer board substrate 12, apatterned resistive material 13 disposed on the substrate 12, andinterconnects 14 and 16. Backer board may be any of a number ofmaterials, but in the preferred embodiment it is formed of a cementousmaterial, and which is designed to underlay tile or other floor finishmaterials. One such product is known as Hardy Board®.

In one embodiment the patterned resistive film is a graphite impregnatedsol-gel material such as that manufactured by either ThermoCeramix, Inc.of Shirley Mass. or Datec Coating Corporation of Milton, Ontario,Canada. The resistive material is applied directly to the backer boardthrough a means of spraying, painting or silk screening onto the surfaceof the substrate that will support the tile or other outer finishmaterial. Other methods of applying a resistor include the thermalspraying of the resistive material. The resistive material could be acontinuous layer covering the entire surface, but is preferably appliedin a pattern to reduce the amount of material required to provide thenecessary power.

In thermal spray, a material in powder or wire form is fed to a heatsource where it is melted into fine droplets. The heat source can becreated by combustion of fuel gases, an electric arc, or ionized plasma.The droplets are accelerated with a carrier gas and directed towards aprepared surface. The droplets impact the surface and freezeinstantaneously. By traversing the spray apparatus repeatedly over thesurface, a coating is built up.

The coatings are deposited using resistive metals or electro conductiveceramics. When metals are used, which is the case when the substrate ismica, the metal is melted in a conventional thermal spray system andsubjected to a reactive gas such as oxygen when the metal is in themolten state. The metal forms reaction products such as metal oxidesthat are incorporated into the deposited coating. The coating will thencomprise the free metal starting material together with some proportionof metal oxides that will tend to boost the coating resistivity. In thisway, a heater with substantially increase resistivity is formed into acoating.

Heater starting materials are typically nickel-chrome alloys,iron-chrome alloys, titanium, titanium oxide or zirconium diboride. Theheater coating is typically designed to form a pattern that determinesthe electrical resistance by balancing a combination of the geometricfactors of element path length, element thickness, and element widthwith material factor of element resistivity.

The resistive film is selected to embody a resistance value thatprovides the necessary power as expressed in watts per square inch orwatts per square foot. This sheet resistance value is affected by acombination of material formulation and thickness of the sol-gel as iswell-known to those of skill in the art, including the manufacturers ofthe material.

In most instances after the sol-gel resistive material is applied, itmust be cured to a finished state by heating. The parameters of thecuring process vary according to the resistive material selected, andthe invention is not limited to any particular curing process. Those ofskill in the art will appreciate the heating/curing process must becontrolled so to adequately heat the uncured resistive material on thesurface of the cement backer board and also so as not to affect thecomposite materials within the underlying backer board. One preferredcuring method employs the use of an infra red heater, which isparticularly well-suited as it can be readily controlled to heatprimarily the resistive film and surface of the backer board withoutoverheating the body of the backer board.

After the resistor material is applied and cured, spaced apartelectrodes or bus-bars are applied to apply a voltage across theresistor. A protective coating 15 such as Teflon® or silicon is thenapplied over the resistor to protect from moisture and to provide anelectrical insulation.

An important feature of the invention with the use of the cement backerboard is that the backer board provides an excellent means ofconnectivity. Affixing fasteners such as threaded screws can be utilizedto make safe and secure electrical connections. The backer board servesas an excellent heat and electrical insulator in the invention.

The use of mica coated heaters can also be utilized by placing the micaheater between the cement backer board and the outer material 18 such astile, linoleum or laminate as shown in FIG. 4, all of which aretypically supported on a subfloor 17. This method requires an additionaladhesive layer; one layer 19 adhering the mica to the backer board, andone adhesive layer 20 adhering the top layer 18 to the mica surface.This method is still preferable to the existing products using heatedwater or wire woven fabrics that take up space and waste energy.

Referring to FIG. 7 individual tiles are assembled into a heatingassembly by placing two tiles adjacent each other with their respectiveelectrical contacts 15 and 16 overlapping. In the embodiment shown theconnectors are connected by screw 23 which is driven through thecontacts and into the underlying backer board. In alternativeembodiments the contacts could also be connected by adhesives or in anyother suitable manner.

Referring to FIGS. 5 and 6 another embodiment is shown at 50. In thisembodiment the resistive layer 52 is a rectilinear layer rather than apattern as in the first embodiment. In this embodiment the contacts 54and 56 are in the form of long conductive strips that are placed incontact with the resistive material and held in place by a conductiveadhesive. The individual tiles are assembled into a floor by placing theedges adjacent one another and interconnecting the conductive strips 54and 56.

In the embodiments described above the individual heating units havebeen connected in series. Heating units receive current from oneadjacent heating unit and provide current to another adjacent heatingunit by connection of contacts as described above. In other embodimentsthe heating units are connected to the power source in a parallelarrangement. The advantage of connecting the heating units in parallelis apparent—the failure of a single heating unit will not adverselyaffect the remaining heating units. The parallel connection of heatingunits can be achieved in any suitable manner, and various arrangementsfor doing so are well-understood by those of skill in the art. The keydistinction is that the electrical contacts on each heating unit areconnected directly to an electrical supply rather than through anadjacent heating unit. This method of connection can also provideadditional advantage in that a lower voltage is required to power theheating units.

In one such embodiment individual heating units are adhered to a backerboard as described above. Rather than each unit being electricallyconnected in series to the adjacent units, each unit is electricallyconnected in parallel to a pair of transverse buses. Referring to FIG.______, in one embodiment the heating unit includes a number ofindividual heating units adhered to the surface of an underlyingsupport. A series of alternating power and ground electrical buses______ extend across the support and connect to supply and groundconductors ______ and ______. Each of the individual heating units isconnected in parallel to the electrical buses. In this embodiment thetransverse electrical buses are connected to a pair of conductors - - -and - - - , one on each side of the panel. In this embodiment eachlateral row of heating units is connected in parallel, preventing asignificant loss of heating capacity in the event of a failure of one ofthe heating units.

While the invention has been described in terms of the preferredembodiments, those of skill in the arts will appreciate that thoseembodiments can be varied in detail and arrangement without departingfrom the scope of the invention.

1. A heater comprising: an insulative substrate; an electricallyresistive material on a major surface of the substrate; at least onecontact terminal in contact with the resistive material; and, adecorative layer covering the resistive material.
 2. A heater accordingto claim 1 further comprising an underlying surface, and the insulativesubstrate mounted on the underlying surface.
 3. A heater according toclaim 5 wherein the insulative substrate is mica.
 4. A radiant heatingsystem according to claim 1 wherein the insulative substrate is formedfrom a cellulosic material.
 5. A heater according to claim 1 wherein theinsulative substrate is formed of a material selected from the groupconsisting of portland cement, gypsum, cementous materials, compositematerials, polymeric materials, glass, ceramics, and minerals.
 6. Aradiant heating system according to claim 1 wherein the insulativesubstrate is formed of a water-resistant material.
 7. A heating systemaccording to claim 1 further comprising a plurality of electricallyinterconnected members, each member comprising: an insulative substrate;a patterned resistive material on a major surface of the substrate; atleast one contact terminal in contact with the resistive material on thesubstrate; and, a decorative layer covering the resistive material.
 8. Aheater according to claim 1 further comprising a controller, atemperature sensor in communication with a controller, the controlleroperable to regulate electrical current to the resistive materialresponsive to a signal from the temperature sensor.
 9. A heateraccording to claim 1 wherein the resistive material forms a serpentinepattern having first and second ends, and the at least one contactterminal comprises a contact terminal connected to each of the first andsecond serpentine pattern end.
 10. A radiant heating system according toclaim 1 wherein the patterned resistive material comprises a rectilinearpattern having first and second opposed edges, and the at least onecontact terminal comprises a contact terminal connected to each of thefirst and second opposed edges.
 11. A radiant heating system accordingto claim 10 wherein the contact terminal connected to each of the firstand second opposed edges comprises an elongate contact terminal.
 12. Aradiant heating system according to claim 1 wherein the resistivematerial comprises a graphite-containing material.
 13. A radiant heatingsystem according to claim 1 wherein the resistive material comprises aheat curable resistive material.
 14. A radiant heating system accordingto claim 7 wherein each at least one contact terminal is positioned tocontact a contact terminal of an adjacent member.
 15. A heating systemaccording to claim 7 wherein the plurality of electricallyinterconnected members connected in series.
 16. A heating systemaccording to claim 7 wherein the plurality of electricallyinterconnected members connected in parallel.
 17. A heater according toclaim 1 wherein the contact terminal is a conductive material inelectrical contact with the resistive material.
 18. A heater accordingto claim 1 wherein the contact terminal comprises a portion of theresistive material.